Contact conductive feature formation and structure

ABSTRACT

Generally, the present disclosure provides example embodiments relating to conductive features, such as metal contacts, vias, lines, etc., and methods for forming those conductive features. In an embodiment, a barrier layer is formed along a sidewall. A portion of the barrier layer along the sidewall is etched back by a wet etching process. After etching back the portion of the barrier layer, an underlying dielectric welding layer is exposed. A conductive material is formed along the barrier layer.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No.16/032,416, now U.S. Pat. No. 10,580,693, filed on Jul. 11, 2018, whichapplication is hereby incorporated herein by reference

BACKGROUND

The semiconductor integrated circuit (IC) industry has experiencedexponential growth. Technological advances in IC materials and designhave produced generations of ICs where each generation has smaller andmore complex circuits than the previous generation. In the course of ICevolution, functional density (e.g., the number of interconnecteddevices per chip area) has generally increased while geometry size(e.g., the smallest component (or line) that can be created using afabrication process) has decreased. This scaling down process generallyprovides benefits by increasing production efficiency and loweringassociated costs.

Accompanying the scaling down of devices, manufacturers have begun usingnew and different materials and/or combination of materials tofacilitate the scaling down of devices. Scaling down, alone and incombination with new and different materials, has also led to challengesthat may not have been presented by previous generations at largergeometries.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a flow chart of an example method for forming conductivefeatures in accordance with some embodiments

FIGS. 2 through 12 are cross-sectional views of respective intermediatestructures during an example method for forming conductive features inaccordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Generally, the present disclosure provides example embodiments relatingto conductive features, such as metal contacts, vias, lines, etc., andmethods for forming those conductive features. In some examples, abarrier layer and/or welding layer formed in an opening through adielectric layer is pulled-back (e.g., etched) to have a heightdifference in the opening that is below the top surface of thedielectric. Accordingly, a pull-back (e.g., etch) is performed to removeredundant structures of the barrier layer and/or welding layer atcorners of the opening to improve profile control and dimensionaccuracy. Among other things, this helps to reduce a formation of voidsduring the depositing of a conductive material on the barrier layerand/or adhesion.

Example embodiments described herein are described in the context offorming conductive features in Front End of the Line (FEOL) and/orMiddle End of the Line (MEOL) processing for transistors.Implementations of some aspects of the present disclosure may be used inother processes and/or in other devices. For example, exampleembodiments may be implemented in Back End of the Line (BEOL)processing. Some variations of the example methods and structures aredescribed. Although method embodiments may be described in a particularorder, various other method embodiments may be performed in any logicalorder and may include fewer or more steps than what is described herein.In some figures, some reference numbers of components or featuresillustrated therein may be omitted to avoid obscuring other componentsor features; this is for ease of depicting the figures.

FIG. 1 depicts an exemplary flow diagram of a process 100 performed toform a semiconductor device structure in accordance with someembodiments. FIGS. 2 through 12 illustrate views of respectiveintermediate structures at respective stages during an example methodfor forming conductive features in accordance with some embodiments. Theintermediate structures, as described in the following, are used in theimplementation of Field Effect Transistors (FETs). Other structures maybe implemented in other example embodiments.

As illustrated in the figures and described herein, the devices areField Effect Transistors (FETs), which may be planar FETs or FinFETs. Inother implementations, the devices can include Vertical Gate All Around(VGAA) FETs, Horizontal Gate All Around (HGAA) FETs, bipolar junctiontransistors (BJTs), diodes, capacitors, inductors, resistors, etc. Inaccordance with planar FETs and/or FinFETs, gate stacks 32 are formed onactive areas of the semiconductor substrate 30, as shown in FIG. 2. Inplanar FETs, the active areas can be a portion at the top surface of thesemiconductor substrate 30 delineated by isolation regions. In FinFETs,the active areas can be three-dimensional fins protruding from betweenisolation regions on the semiconductor substrate 30. The semiconductorsubstrate 30 can be or include a bulk semiconductor substrate, asemiconductor-on-insulator (SOI) substrate, or another substrate. Thesemiconductor material of the semiconductor substrate 30 can include orbe an elemental semiconductor like silicon (e.g., crystalline siliconlike Si<100> or Si<111>) or germanium, a compound or alloysemiconductor, the like, or a combination thereof. The semiconductormaterial of the semiconductor substrate 30 may be doped or undoped, suchas with a p-type or an n-type dopant. Other substrates, such as amulti-layered or gradient substrate may also be used. In someembodiments, the semiconductor material of the semiconductor substratemay include an elemental semiconductor like silicon (Si) and germanium(Ge); a compound semiconductor including silicon carbide, galliumarsenic, gallium phosphide, indium phosphide, indium arsenide, and/orindium antimonide; an alloy semiconductor including SiGe, GaAsP, AlInAs,AlGaAs, GalnAs, GaInP, and/or GaInAsP; or a combination thereof.

The gate stacks 32 can be operational gate stacks like in a gate-firstprocess or can be dummy gate stacks like in a replacement gate process.In the replacement gate process, each gate stack 32 can comprise adielectric layer over the active area, a gate layer over the dielectriclayer, and, in some instances, a mask layer over the gate layer, whichgate stack 32 is later replaced by a metal gate structure that caninclude a high-k dielectric material. A high-k dielectric material mayhave a k value greater than about 7.0, and may include a metal oxide ofor a metal silicate of hafnium (Hf), aluminum (Al), zirconium (Zr),lanthanum (La), magnesium (Mg), barium (Ba), titanium (Ti), lead (Pb),multilayers thereof, or a combination thereof. The gate layer (e.g.,gate electrode) may include or be silicon (e.g., polysilicon, which maybe doped or undoped), a metal-containing material (such as titanium,tungsten, aluminum, ruthenium, TiN, TaN, TaC, Co, a combination thereof(such as a silicide (which may be subsequently formed), or multiplelayers thereof. The mask layer may include or be silicon nitride,silicon oxynitride, silicon carbon nitride, the like, or a combinationthereof. Processes for forming or depositing the dielectric layer, gatelayer, and mask layer include thermal and/or chemical growth, ChemicalVapor Deposition (CVD), Plasma-Enhanced CVD (PECVD), Molecular-BeamDeposition (MBD), Atomic Layer Deposition (ALD), Physical VaporDeposition (PVD), and other deposition techniques. The layers for thegate stacks 32 may then be patterned to be the gate stacks 32, forexample, using photolithography and one or more etch processes. Forexample, a photo resist can be formed on the mask layer (or gate layer,for example, if no mask layer is implemented), such as by using spin-oncoating, and can be patterned by exposing the photo resist to lightusing an appropriate photomask. Exposed or unexposed portions of thephoto resist may then be removed depending on whether a positive ornegative resist is used. The pattern of the photo resist may then betransferred to the layers of the gate stacks 32, such as by using one ormore suitable etch processes. The one or more etch processes may includea reactive ion etch (RIE), neutral beam etch (NBE), the like, or acombination thereof. The etching may be anisotropic. Subsequently, thephoto resist is removed in an ashing or wet strip processes, forexample.

Gate spacers 34 are formed along sidewalls of the gate stacks 32 andover the active areas on the semiconductor substrate 30. The gatespacers 34 may be formed by conformally depositing one or more layersfor the gate spacers 34 and anisotropically etching the one or morelayers, for example. The gate spacers 34 may include or be siliconnitride, silicon oxynitride, silicon carbon nitride, the like,multi-layers thereof, or a combination thereof.

Source/drain regions 36 are formed in the active regions on opposingsides of the gate stack 32. In some examples, the source/drain regions36 are formed by implanting dopants into the active areas using the gatestacks 32 and gate spacers 34 as masks. Hence, source/drain regions 36can be formed by implantation on opposing sides of each gate stack 32.In other examples, the active areas may be recessed using the gatestacks 32 and gate spacers 34 as masks, and epitaxial source/drainregions 36 may be epitaxially grown in the recesses. Epitaxialsource/drain regions 36 may be raised in relation to the active area.The epitaxial source/drain regions 36 may be doped by in situ dopingduring the epitaxial growth and/or by implantation after the epitaxialgrowth. The epitaxy source/drain regions 36 may include or be silicongermanium, silicon carbide, silicon phosphorus, silicon carbonphosphorus, germanium, a III-V compound semiconductor, a II-VI compoundsemiconductor, or the like. The epitaxy source/drain regions 36 may beformed in the recesses by an appropriate epitaxial growth or depositionprocess. In some examples, epitaxy source/drain regions 36 can havefacets, which may correspond to crystalline planes of the substrate 30.Hence, source/drain regions 36 can be formed by epitaxial growth, andpossibly with implantation, on opposing sides of each gate stack 32.

A first interlayer dielectric (ILD) 38 is formed between the gate stacks32 and over the semiconductor substrate 30. The first ILD 38 isdeposited over the active areas, gate stacks 32, and gate spacers 34. Insome examples, an etch stop layer (not shown) may be conformallydeposited over the active areas, gate stacks 32, and gate spacers 34.Generally, an etch stop layer can provide a mechanism to stop an etchingprocess when forming, e.g., contacts or vias. An etch stop layer may beformed of a dielectric material having a different etch selectivity fromadjacent layers, for example, the first ILD 38. The etch stop layer maycomprise or be silicon nitride, silicon carbon nitride, silicon carbonoxide, carbon nitride, the like, or a combination thereof, and may bedeposited by chemical vapor deposition (CVD), plasma enhanced CVD(PECVD), atomic layer deposition (ALD), or another deposition technique.The first ILD 38 may comprise or be silicon dioxide, a low-k dielectricmaterial (e.g., a material having a dielectric constant lower thansilicon dioxide), silicon oxynitride, phosphosilicate glass (PSG),borosilicate glass (BSG), borophosphosilicate glass (BPSG), undopedsilicate glass (USG), fluorinated silicate glass (FSG), organosilicateglass (OSG), SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, siliconcarbon material, a compound thereof, a composite thereof, the like, or acombination thereof. The first ILD 38 may be deposited by spin-on, CVD,Flowable CVD (FCVD), PECVD, physical vapor deposition (PVD), or anotherdeposition technique. The first ILD 38 can be planarized after beingdeposited. A planarization process, such as a Chemical Mechanical Polish(CMP), may be performed to planarize the first ILD 38.

A second interlayer dielectric (ILD) 40 is formed over the first ILD 38,as shown in FIG. 3. The second ILD 40 is deposited over the first ILD38. The second ILD 40 is made by similar material utilized to form thefirst ILD 38. The second ILD 40 can be planarized, such as by a CMP,after being deposited. A thickness of the first and second ILD 38, 40can be in a range from about 50 nm to about 1200 nm. A combinedthickness of the first and second ILD 38, 40 can be in a range fromabout 100 nm to about 2400 nm.

Referring back to the process 100 depicted in FIG. 1, at operation 106,a patterning process is performed to form openings 42, 44, and 46through the second ILD 40 and the first ILD 38, as shown in FIG. 4. Thefirst opening 42 exposes a gate stack 32 and an adjoining source/drainregion 36. The first opening 42 is therefore for forming a buttedconductive feature between the exposed gate stack 32 and adjoiningsource/drain region 36. The second opening 44 exposes a source/drainregion 36, and is therefore for forming a conductive feature to theexposed source/drain region 36. The third opening 46 exposes a gatestack 32, and is therefore for forming a conductive feature to theexposed gate stack 32. The openings 42, 44, and 46 may be formed using,for example, appropriate photolithography and etching processes.

At operation 108, a welding layer 50 is formed in the openings 42, 44,and 46, followed by a first barrier layer 52 is conformally formedthereon. In some embodiments, the welding layer 50 is also called awetting layer or a glue layer. The welding layer 50 is patterned so thatthe welding layer 50 is formed on the sidewalls of the openings 42, 44,46 while exposing the underlying source/drain region 36, as shown inFIG. 5, for the later annealing process. Subsequently, the first barrierlayer 52 is conformally formed on the welding layer 50 in the openings42, 44, and 46 as well as on the exposed source/drain regions 36,exposed gate stacks 32, sidewalls of second ILD 40, and the top surfaceof the second ILD 40, as shown in FIG. 6. In some embodiments, the firstbarrier layer 52 is also called an adhesion layer or an anti-reflectioncoating (ARC) layer as needed.

In one example, the welding layer 50 may be or comprises a dielectricmaterial comprising silicon, such as silicon oxide, silicon nitride,silicon carbide, silicon oxycarbide, silicon oxynitride the like, ormultilayers thereof. The welding layer 50 may be formed by PECVD, lowpressure CVD (LPCVD), Flowable CVD, ALD, or another depositiontechnique. It is believed that the dielectric material provided by thewelding layer 50 can provide good interface bonding between the ILDs 38,40 and the first barrier layer 52, which will be discussed furtherbelow, with good interface adhesion and integration. The dielectricmaterial from the welding layer 50 can include silicon elements andother elements, such as nitrogen, oxygen and/or carbon elements. Thus,the silicon elements from the welding layer 50 may have a bonding energyto bond on the first and second ILD 38, 40, which also can have siliconelements. Thus, by utilizing the welding layer 50 of a dielectricmaterial comprising silicon, good interface adhesion and integration maybe obtained.

Furthermore, as the welding layer 50 selected herein is a dielectricmaterial, the welding layer 50 is patterned to expose the underlyingsource/drain region 36. Thus, the first barrier layer 52 later formedthereon can be in contact with the source/drain region 36. As a result,during the subsequent annealing process, the source/drain region 36 maybe converted to a silicide material by chemical reaction between thefirst barrier layer 52 and the source/drain region 36.

In some embodiments, the welding layer 50 formed herein in FIG. 5 is asilicon nitride material having a thickness in a range from about 0.5 nmto about 10 nm.

The first barrier layer 52 may be or comprise a metal containingmaterial, for example, titanium, cobalt, nickel, the like or acombination thereof, and may be deposited by ALD, CVD, or anotherdeposition technique. The first barrier layer 52 may be or comprisetitanium nitride, titanium oxide, tantalum nitride, tantalum oxide, thelike, or a combination thereof, and may be deposited by ALD, CVD, oranother deposition technique.

At operation 110, an annealing process can be performed to facilitatethe reaction of the source/drain regions 36 with the first barrier layer52 to form silicide regions 55 (e.g., a silicide region with a metalcontaining material reacted with a semiconductor material (e.g., Siand/or Ge)) on the source/drain regions 36, as shown in FIG. 7. In someexamples, when the first barrier layer 52 is a layer of titanium ortitanium nitride, the silicide region 55 is a titanium silicidematerial. Although the silicide regions 55 are only shown formed on thesource/drain regions 36 in FIG. 7, it is noted that the silicide region55 may be formed in other locations/places, such as above the gatestacks 32 or other locations as needed on the substrate 30.

At operation 112, after the silicide regions 55 are formed, the firstbarrier layer 52 formed on the substrate 30 may be removed, as shown inFIG. 8. The first barrier layer 52 can be removed from the substrate 30by suitable etching techniques, such as a reactive ion etch (RIE),neutral beam etch (NBE), wet etching, or another etching process. Insome examples, the welding layer 50 remains on the substrate 30 forinterface protection.

At operation 114, a second barrier layer 58 is formed on the weldinglayer 50, the exposed silicide region 55, the exposed first and secondILD 38, 40, and other exposed regions of the substrate 30, as shown inFIG. 9. The second barrier layer 58 may be similar to the first barrierlayer 52 conformally deposited on the welding layer 50 and the substrate30. The second barrier layer 58 may be or comprise titanium nitride,titanium oxide, tantalum nitride, tantalum oxide, the like, or acombination thereof, and may be deposited by ALD, CVD, or anotherdeposition technique. In some examples, the second barrier layer 58 hasa thickness in a range from 5 nm to about 80 nm.

In one example, the second barrier layer 58 is selected from a materialsharing a similar element with the welding layer 50 so that theinterface adhesion between the welding layer 50 and the second barrierlayer 58 is enhanced. For example, when the welding layer 50 includessilicon elements and other elements, such as nitrogen, oxygen and/orcarbon elements, the silicon elements may have a bonding energy to bondon the first and second ILD 38, 40, which also can have siliconelements. Meanwhile, the other elements (e.g., nitrogen, oxygen and/orcarbon elements) from the welding layer 50 bonds to the second barrierlayer 58, which is selected to at least have nitrogen, oxygen, or carbonelements. Thus, well selection of the materials between the weldinglayer 50 and the second barrier layer 58 can enhance the interfaceintegration and adhesion therebetween, so as to improve the overalldevice structure integrity and performance. Thus, by utilizing thewelding layer 50 of a dielectric material comprising silicon and otherelements similar to the elements from the second barrier layer 58, goodinterface adhesion and integration may be obtained.

In operation 116, a pull-back process is performed to remove a portionof the second barrier layer 58 as well as a portion of the welding layer50 from the substrate 30, as shown in FIG. 10. The pull-back process isan etching process including dry etching process or wet etching process.

In some embodiments, the pull-back process as described here to etch thesecond barrier layer 58 is a wet etching process so as to remove anupper portion of the second barrier layer 58 close to the corners of theopenings 42, 44, 46 from the substrate 30. The pull-back processincludes removing the second barrier layer 58 to a depth 88 below a topsurface 67 of the second ILD 40, which removes the excess second barrierlayer, which may be accumulated at the corner 59 of the opening 42, 44,46. A top surface of the second barrier layer 58 is below the topsurface 67 of the second ILD 40 as well as a top surface of the weldinglayer 50. By removing the upper portions of the second barrier layer 58at upper regions (e.g., corners 59) of the openings 42, 44, and 46, awider width 80 of the openings 42, 44, 46, without both the weldinglayer 50 and the second barrier layer 58, can be obtained compared tothe shorter width 81 at the welding layer 50 and the even shorter width82 at the second barrier layer 58. It is noted that a portion of thewelding layer 50 is also removed during the pull-back process, which mayassist widening the width 80 of the openings 42, 44, 46 for thesubsequent processes. The wider widths 80, 81 of the openings 42, 44, 46can provide a wider process window for the conductive metal fill layersubsequently formed therein with less likelihood of voids or seamsformed therein. In some examples, the shorter width 81 is less than thewider width 80 by an amount in a range from about 5% to about 15% of thewider width 80, and the even shorter width 82 is less than the widerwidth 80 by an amount in a range from about 8% to about 30% of the widerwidth 80.

In some examples, the pull-back process is a wet etch process. The wetetch process can include immersing the substrate 30 in a solutioncomprising deionized (DI) water and a suitable chemical. The chemicalreaction between the solution and the second barrier layer 58predominately etches the second barrier layer 58 and a portion of thewelding layer 50 until a predetermined process time period is reached orthe desired depth 88 is formed in the openings 42, 44, 46, as shown inFIG. 10. Suitable examples of the chemicals included in the DI waterinclude hydrogen peroxide (H₂O₂), ammonium hydroxide (NH₄OH), HNO₃,H₂SO₄, HCl, dilute-HF, and the like. In some examples, the chemical usedin the DI water to etch the second barrier layer 58 includes H₂O₂. It isbelieved that H₂O₂ in the DI water may react with the Ti/Ta elementsfrom the second barrier layer 58 so as to remove a portion of the secondbarrier layer 58 from the substrate 30.

The chemical in the DI water may have a concentration from 0.1% to 50%.The solution, during the immersion, may be at a temperature in a rangefrom about 20° C. to about 90° C. The substrate 30 may be immersed inthe solution for a duration in a range from about 5 seconds to about 120seconds to form the depth in a range from 1 nm to 50 nm. Thesemiconductor substrate 30 may optionally be rinsed in isopropyl alcohol(IPA) following the immersion in the solution to dry the substrate 30.

In some examples, the second barrier layer 58 is etched back (e.g.,pulled back) to expose a top portion 54 of the welding layer 50 in theopenings 42, 44, 46. The top portion 54 of the welding layer 50 exposedby the second barrier layer 58 has a depth 60 of between about 15 nm andabout 25 nm. As discussed above, excess second barrier layer 58 formedat corners 59 of the openings 42, 44, 46 may potentially increase thelikelihood of early closure of the openings 42, 44, 46 in followingdeposition processes. However, the second barrier layer 58 may enablethe nucleation and growth of the metal materials of the metal conductivefilling material 66 subsequently filled therein. Thus, a balance of thethickness formed for the second barrier layer 58 can be modulated toboth enable the growth of the following metal conductive fillingmaterial 66 as well as prevent blocking of the openings 42, 44, 46.Thus, by pulling back the second barrier layer 58 to expose a portion ofthe underlying welding layer 50, the second barrier layer 58 formed atthe corners 59 can be removed, and the top portion of the openings 42,44, 46 can also be widened, which can assist filling the metalconductive filling material 66 therein without early closure to preventvoids. As some amount of the second barrier layer 58 still remains inthe openings 42, 44, 46, nucleation sites and adhesion surfaces alsoremain and can allow the metal elements to adhere thereon in thesubsequent deposition process. In some examples, the depth 60 of thewelding layer 50 is exposed by the second barrier layer 58, as shown inFIG. 10. In some examples, the depth 60 is in a range from about 15 nmto about 25 nm.

In the examples wherein a dry etching process is used for the pull-backprocess, the dry etching process may include a RIE, NBE, inductivelycoupled plasma (ICP) etch, the like, or a combination thereof. Exampleetchant gases that can be used for a plasma etch process include ahalogen containing gas or another etchant gas. A flow rate of theetchant gas(es) of a plasma etch process may be in a range from about 10sccm to about 100 sccm. A plasma etch process may implement a DCsubstrate bias in a range from about 10 kV to about 500 kV. A power of aplasma etch process may be in a range from about 200 W to about 2000 W.A pressure of a plasma etch process may be in a range from about 5 mTorrto about 50 mTorr. The depth 88 of the pull-back can be controlled by aduration of the etch process used for the pull-back. A duration of aplasma etch process can be in a range from about 10 seconds to about 600seconds for achieving the depth 88 in a range from 15 nm and about 35 nmin some examples.

At operation 118, a metal conductive filling material 66 is formed inthe openings 42, 44, and 46 and on the second barrier layer 58 and thetop portion 54 of the welding layer 50, as shown in FIG. 11. The metalconductive filling material 66 may be or comprise a metal, such ascobalt, tungsten, copper, aluminum, gold, silver, alloys thereof, thelike, or a combination thereof, and may be deposited by CVD, ALD, PVD,or another deposition technique. The pull-back of the second barrierlayer 58 can permit larger dimensions (e.g., the widths 80, 81) at upperportions of the openings 42, 44, and 46 or compared to the lower portionsecond barrier layer 58 having a shorter width 82 in the openings 42,44, 46. Thus, the larger dimensions at the upper portions of theopenings 42, 44, 46 can permit the metal conductive filling material 66to fill the openings 42, 44, and 46 without a void in the metalconductive filling material 66 in the openings 42, 44, and 46.

In some examples, excess metal conductive filling material 66 may beremoved, as shown in FIG. 12. After the metal conductive fillingmaterial 66 is deposited, excess metal conductive filling material 66over the top surface 67 of the second ILD 40 may be removed by using aplanarization process, such as a CMP, for example. The planarizationprocess may remove excess metal conductive filling material 66 fromabove the top surface 67 of the second ILD 40. This forms conductivefeatures 70, 72, 74 comprising the metal conductive filling material 66in the openings 42, 44, and 46, respectively. Top surfaces of theconductive features 70, 72, 74 and second ILD 40 may be coplanar.Accordingly, conductive features 70, 72, 74 including the metalconductive filling material 66, second barrier layers 58 and weldinglayer 50 (and, possibly, silicide regions 55) may be formed tocorresponding gate stacks 32 and/or source/drain regions 36. As apparentfrom FIG. 12, the widths of the metal conductive filling material 66 ofthe conductive features 70, 72, and 74 at the top surfaces thereof canbe increased by pulling back the second barrier layer 58 and the weldinglayer 50, which can increase a surface area to which respectivesubsequent conductive features can make contact.

As shown by the preceding, aspects of some embodiments can be applied toFront End Of the Line (FEOL) and Middle End Of the Line (MEOL)processes. Conductive features 70, 72, and 74, including the processesby which the conductive features 70, 72, and 74 were formed, canimplement aspects of various embodiments in FEOL and/or MEOL. Otherconductive features formed in FEOL and/or MEOL processes may similarlyincorporate aspects according to some embodiments. For example,replacement gate stacks can be formed according to some embodiments. Forreplacement gate stacks, for example, conformal layers, such as adielectric layer and/or work-function tuning layer(s), that are formedwhere a dummy gate stack was removed can be deposited and pulled backaccording to the same or similar processes illustrated and describedabove. In other examples, aspects of the foregoing can be incorporatedin conductive features formed in intermetallization dielectrics (IMDs)in Back End Of the Line (BEOL) processing.

Some embodiments can achieve advantages. By removing a portion of abarrier layer at an upper portion of an opening or recess, conductivematerial that will form a conductive feature can be more easilydeposited in the opening or recess without a void being formed in theopening or recess. Particularly when dimensions of conductive featuresare small, voids in conductive features can cause higher resistance ofthe conductive features or complete failure of the conductive feature,such as by failing to establish electrical contact. Hence, mitigatingvoid formation may be advantageous, particularly in small technologynodes, such as advanced technologies with small dimensions. Further,heights of welding layers and barrier layers in conductive features canbe tuned based on different process control and device performancerequirements.

In an embodiment, a method for a semiconductor process includes forminga dielectric welding layer along a sidewall of an opening in adielectric layer, forming a barrier layer on the dielectric weldinglayer, etching back a portion of the barrier layer to expose a sidesurface of an upper portion of the dielectric welding layer and forminga conductive material on the side surface of the upper portion of thedielectric welding layer and on the barrier layer. In an embodiment, thebarrier layer is wet etched using a solution including at least one ofH₂O₂, H₂SO₄, HNO₃, NH₄OH, or a combination thereof. In an embodiment, aportion of the conductive material is in direct contact with the sidesurface of the upper portion of the dielectric welding layer. In anembodiment, the barrier layer includes at least one of titanium nitride,titanium oxide, tantalum nitride and tantalum oxide. In an embodiment,the dielectric welding layer is a silicon-containing dielectricmaterial. In an embodiment, the dielectric welding layer includes atleast one of silicon oxide, silicon nitride, silicon carbide, siliconoxycarbide and silicon oxynitride. In an embodiment, the side surface ofthe upper portion of the dielectric welding layer exposed by the etchingback of the portion of the barrier layer is exposed to a depth in arange from about 15 nm to about 25 nm. In an embodiment, a top surfaceof the barrier layer is lower than a top surface of the dielectricwelding layer on the sidewall of the opening of the dielectric layer.

In another embodiment, a structure includes a dielectric layer having asidewall, the dielectric layer being over a substrate, a dielectricwelding layer along the sidewall, the dielectric welding layer exposingan upper portion of the sidewall, a barrier layer along the dielectricwelding layer, the barrier layer exposing an upper portion of thedielectric welding layer, and a conductive material along the barrierlayer and along the respective upper portions of the sidewall and thedielectric welding layer. In an embodiment, the conductive material hasa top width in contact with the dielectric welding layer wider than abottom width in contact with the barrier layer. In an embodiment, theconductive material is in direct contact with the upper portion of thedielectric welding layer. In an embodiment, a depth is defined betweenrespective top surfaces of the dielectric welding layer and the barrierlayer, wherein the depth is from about 15 nm to 25 nm. In an embodiment,a top surface of the barrier layer is below a top surface of thedielectric welding layer. In an embodiment, the conductive materialincludes at least one of cobalt, tungsten, copper, aluminum, gold andsilver. In an embodiment, a silicide region is formed along a bottom ofthe barrier layer under the conductive material. In an embodiment, thedielectric welding layer is a silicon-containing dielectric material. Inan embodiment, the dielectric welding layer includes at least one ofsilicon oxide, silicon nitride, silicon carbide, silicon oxycarbide andsilicon oxynitride. In an embodiment, the barrier layer includes atleast one of titanium nitride, titanium oxide, tantalum nitride andtantalum oxide.

In yet another embodiment, a structure includes a dielectric layer, aconductive material formed in the dielectric layer and laterally boundby a barrier layer, and a dielectric welding layer laterally between thebarrier layer and the dielectric layer, wherein the barrier layer andthe dielectric welding layer have mismatched heights along a sidewall ofthe dielectric layer. In an embodiment, the mismatched heights define astep height in a range from 15 nm to 25 nm.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device comprising: a source/drainregion; a first gate structure adjacent the source/drain region; adielectric layer over the first gate structure and the source/drainregion; and a contact structure extending through the dielectric layerto the source/drain region, the contact structure comprising: a weldinglayer, wherein an upper surface of the welding layer is lower than anupper surface of the dielectric layer, wherein the welding layer and thedielectric layer have a common element; a barrier layer on the weldinglayer, wherein an upper surface of the barrier layer is lower than theupper surface of the welding layer, wherein the welding layer and thesecond barrier layer have a common element; and a metal conductivefilling material over the second barrier layer, wherein the secondbarrier layer completely separates the metal conductive filling materialfrom the source/drain region.
 2. The semiconductor device of claim 1,wherein the upper surface of the barrier layer is recessed a distance ina range from about 15 nm to about 25 nm below the upper surface of thewelding layer.
 3. The semiconductor device of claim 1, wherein thedielectric layer comprises a plurality of dielectric layers.
 4. Thesemiconductor device of claim 1, wherein a first width is from a firstsidewall of the dielectric layer to a second sidewall of the dielectriclayer, wherein a second width is from a first inner sidewall of thewelding layer to a second inner sidewall of the welding layer, whereinsecond width is in a range from 5% to 15% less than the first width. 5.The semiconductor device of claim 1, wherein a first width is from afirst sidewall of the dielectric layer to a second sidewall of thedielectric layer, wherein a second width is from a first inner sidewallof the barrier layer to a second inner sidewall of the barrier layer,wherein second width is in a range from 8% to 30% less than the firstwidth.
 6. The semiconductor device of claim 1, wherein the secondbarrier layer directly contacts the source/drain region.
 7. Thesemiconductor device of claim 1, wherein the second barrier layercomprises nitrogen elements, oxygen elements, or carbon elements.
 8. Asemiconductor device comprising: a source/drain region, the source/drainregion comprising a silicide region; a first gate structure adjacent thesource/drain region; one or more dielectric layers over the first gatestructure and the source/drain region; and a contact structure extendingthrough the one or more dielectric layers to the silicide region of thesource/drain region, the contact structure comprising: a welding layer,wherein an upper surface of the welding layer is lower than an uppersurface of the one or more dielectric layers; a barrier layer on thewelding layer and extending over the silicide region, wherein an uppersurface of the barrier layer is lower than the upper surface of thewelding layer, wherein the barrier layer completely covers the silicideregion; and a metal conductive filling material over the second barrierlayer.
 9. The semiconductor device of claim 8, wherein the contactstructure extends from the source/drain region to over the first gatestructure.
 10. The semiconductor device of claim 8, wherein the weldinglayer and a first dielectric layer of the one or more dielectric layershave a common element.
 11. The semiconductor device of claim 8, whereinthe welding layer and the second barrier layer have a common element.12. The semiconductor device of claim 8, wherein the welding layerincludes at least one of silicon oxide, silicon nitride, siliconcarbide, silicon oxycarbide, and silicon oxynitride.
 13. Thesemiconductor device of claim 8, wherein the metal conductive fillingmaterial directly contacts the upper surface of the welding layer andthe upper surface of the barrier layer.
 14. The semiconductor device ofclaim 8, wherein the silicide region directly contacts the barrierlayer.
 15. The semiconductor device of claim 8, wherein the barrierlayer and the silicide region have a common element.
 16. A method for asemiconductor process, the method comprising: forming sharedsource/drain region, a first gate structure, and a second gatestructure, the shared source/drain region being a source/drain regionfor both the first gate structure and the second gate structure, thefirst gate structure comprising a first gate spacer and a first gateelectrode, the second gate structure comprising a second gate spacer anda second gate electrode; forming one or more dielectric layers over thefirst gate structure, the second gate structure, and the source/drainregion; forming a first opening through the one or more dielectriclayers, the first opening exposing the source/drain region, a sidewallof the first gate spacer, and a sidewall of the second gate spacer;forming a welding layer along sidewalls of the first opening in the oneor more dielectric layers, the sidewall of the first gate spacer, andthe sidewall of the second gate spacer, an upper surface of the one ormore dielectric layers being free of the welding layer, wherein thewelding layer and the one or more dielectric layers have a first commonelement; forming a barrier layer on the welding layer, wherein thewelding layer and the barrier layer have a second common element,wherein the barrier layer contacts an upper surface of the one or moredielectric layers; etching back a portion of the welding layer and thebarrier layer to expose a sidewall of the one or more dielectric layersand a sidewall of the welding layer; and forming a conductive materialover the barrier layer.
 17. The method of claim 16, wherein the firstcommon element is silicon.
 18. The method of claim 16, wherein thesecond common element is nitrogen, silicon, or carbon.
 19. The method ofclaim 16, wherein the first opening exposes an upper surface of thefirst gate electrode.
 20. The method of claim 19 further comprising:forming a third gate structure, wherein the one or more dielectriclayers are formed over the third gate structure; and forming a secondopening through the one or more dielectric layers, the second openingexposing an upper surface of the third gate structure, wherein thewelding layer and the barrier layer extends along sidewalls of thesecond opening to the third gate structure.
 21. The method of claim 16,wherein an upper surface of the barrier layer is recessed from an uppersurface of the one or more dielectric layers by an amount in a rangefrom about 15 nm to about 35 nm.